1. Field of the Invention
The present invention relates to a programmable power converter, and, more particularly, the present invention relates to an under-voltage protection circuit for programmable power supplies.
2. Description of the Related Art
Programmable power supplies are developed to provide different constant output voltage levels, such as 5 V, 9 V, 12 V, and 19 V, to power different equipments. Some of them having constant output current characteristic are called chargers which are used to charge batteries. An output current usually has a current limit to ensure that the batteries can be charged under or equal to a safe current that won't damage the batteries.
FIG. 2 shows a characteristic curve of an output voltage VO versus an output current IO for a traditional power supply with constant output current and constant output voltage characteristic. When the output current IO demanded by the output load of the power supply reaches a threshold current IT, the output voltage VO will start to decrease automatically to keep the output current IO as a constant. In a case, the threshold current IT is the maximum value of the characteristic curve. However, as the output voltage VO drops to a too low level, the batteries, especially to lithium batteries, would be damaged permanently due to its over discharging.